In October 1948, Star-Spangled Comics #87 has Merry the Gimmick Girl taking over for poor ol’ Star-Spangled Kid and Stripesy. The story features Merry and Mr. Pemberton, her foster father – but Sylvester and Pat are nowhere to be seen.
The comic industry really seems to have declared itself done with boy sidekicks, with basically just Robin and Speedy left. Timing-wise, this might have to do with Dr. Fredric Wertham’s attack on the comic book industry, begun in May 1948 in the Saturday Review of Literature, though that article itself does not mention anything about homosexual subtext with sidekicks. An article that made Stan Lee sit up and take notice, inserting a 1-page defense in all of Timely (Marvel) Comics of 1948: